Several months ago, for certain "reasons", I had to be in guy mode for a particular errand - that was after nearly six months straight of 24/7 girl mode. I actually had a not-so-mild panic attack in the process. It was horrible... thank god it was only for one hour. Never again. Never.
So be careful, if you've become mostly or completely accustomed to being in girl mode you might find fitting into guy mode more difficult than just "not acting girly"... 🙂